We construct high-quality graphene-based van der Waals devices with narrow superconducting niobium nitride (NbN) electrodes, in which superconductivity and a robust fractional quantum Hall (FQH) state coexist. We find a possible signature for crossed Andreev reflection (CAR) across the superconductor separating two FQH edges. Our observed CAR probabilities in the particlelike fractional fillings are markedly higher than those in the integer and hole-conjugate fractional fillings and depend strongly on temperature and magnetic field unlike the other fillings. Further, we find a filling-independent CAR probability in integer fillings, which we attribute to spin-orbit coupling in NbN allowing for Andreev reflection between spin-polarized edges. These results provide a route to realize novel topological superconducting phases in FQH-superconductor hybrid devices based on graphene and NbN.

中文翻译：

---

分数量子霍尔态中的 Andreev 反射

我们构建了高质量的基于石墨烯的范德华器件，该器件具有窄超导氮化铌 (NbN) 电极，其中超导性和稳健的分数量子霍尔 (FQH) 状态共存。我们发现了跨越超导体的交叉安德烈夫反射 (CAR) 的可能特征，该超导体分隔了两个 FQH 边缘。我们在颗粒状部分填充物中观察到的 CAR 概率明显高于整数和孔共轭部分填充物，并且与其他填充物不同，强烈依赖于温度和磁场。此外，我们在整数填充中发现了与填充无关的 CAR 概率，我们将其归因于 NbN 中的自旋轨道耦合，允许自旋极化边缘之间的安德烈夫反射。